This invention relates to a calibration method for an input section of a color film inspection system which evaluates color original images of a negative film before photographic printing process.
There has been known in the prior art as the color film inspection system of this type the one disclosed in Japanese Patent Laid-open No. 207238/1982 wherein the color images which have been automatically corrected in color and density are displayed on a color monitor. An operator observes the monitored images to evaluate the automatically corrected color images and discriminates the images which are not desirable in density or color-balance or which should not be printed as they are out of focus. Only for those which are difficult to be automatically corrected (color failure, rear light, light sources of different types, etc.), the operator has to manually correct the density and color by a manual operation of a data input section. This system allows even unskilled and inexperienced operators to produce photographs of high quality without necessitating a highly precise color film automatic analyzer. The correction information which is determined by the operator or automatically computed by the system is recorded on a recording medium such as a paper tape or a magnetic tape, and when a color film is mounted on an automatic printer at photographic printing process, the recording medium is read out to control the printing exposure amount with the correction information.
In such a conventional inspection system, however, calibration of the image input section is not taken into account at all thereby presenting difficulties in maintaining precision in inspection against fluctuation in gain or offset.
The inspection by the conventional systems is conducted in the procedure as shown in FIG. 1. A film with original images to be printed, for instances a negative film 100 is illuminated with light from a light source 101 and the whole images are picked up by an image pick up device such as a TV camera 102 and inputted into an image processing circuit 110. The image processing circuit 110 includes a color correction circuit, a gradation conversion table and a negative/positive converter, so that it conducts necessary processing on the video signals from the TV camera 102 to display images of the negative film 100 on a display unit 115 such as a CRT via a display control circuit 113. An operator watches the images displayed on the display unit 115 and if the operator judges the color balance or the density unsatisfactory, corrects the images by manipulating a keyboard 114. The analyzed data of the image processing is recorded on a recording medium 112 such as a magnetic tape, a floppy disc or a paper by a data output device 111. The negative film 100 which has been inspected and corrected in this way is sent to a photographic color printer 120 together with the data recorded on the recording medium 112 by the data output device 111 and the photographic color printer 120 prints the images on a color paper to provide a photograph 121.
In the above described conventional system, the negative film 100 on the display unit 115 is inspected by the operator, but the images on the resultant photograph 121 is printed by the photographic color printer 120 on the color paper. Unless the images displayed on the display unit 115 in the inspection system is accurately corresponded to the photograph 121 printed by the color printer 120, the photograph 121 printed by the color printer 120 is not necessarily optimal even if the images are correctly displayed and corrected optimally at the display unit 115. This presents a difficulty.